The present invention relates to a method for producing
polymethylmethacrylate layers having varying thicknesses.
Polymethylmethacrylate (PMMA) can be used as a photoresist for lithographic structuring with high-energy, ionizing radiation. To this end, a thin PMMA layer is applied to various substrates, which are composed of metallic, semi-conducting, or insulating materials. An "image" is then generated in the PMMA layer utilizing electron beams or through x-ray lithography. After a wet-chemical development, the "image" is converted into a structure of PMMA. This structure represents a positive image.
The resultant PMMA structure can function as a mask for additional fabrication steps. In particular, structures, suitable for micro-electronic and other micro components, can be produced on the substrate. This can be achieved through etching, doping, or deposition of arbitrary, additional materials, including metallic materials.
Similar to the application of a standard photoresist, the application of PMMA layers proceeds in solution, for example, through dribbling or by whirling. Solvents that can be used for this purpose include chlorobenzene and methylisobutylketone.
Although the production of simple, thin photoresist layers are possible, it is not possible to produce uniform, smooth layers, having a thickness per layer of greater than 20 .mu.m, utilizing known solvents. Thick layers created utilizing known solvents exhibit a grainy surface. Moreover, the surface of such thick layers is under a mechanical stress and tends to form cracks. Additionally, for producing thicker layers, a more concentrated and, thus, a more viscous solution of PMMA is required. Such a concentrated solution of PMMA cannot be prepared with known solvents.
Heretofore, a PMMA layer having a thickness greater than 20 .mu.m could only be achieved by gluing thin PMMA foils together utilizing a cyanacrylate adhesive. This process, however, is a very involved, costly and time intensive method. Another possible way to attempt to produce arbitrary structures, having a thickness of more than 20 .mu.m and also having a high aspect ratio, is by utilizing a two-component reaction resins. This technique, among other things, is extremely involved due to the complicated mixing and dosing of the two resin components.